1. Receiver Design for Ultrawideband PPM Communication Systems Vijay Ullal Clemson University July 29, 2004 2004 SURE Program

2. Brief Overview Background Information Description of Receiver Designs Observations and Conclusions Future Work

3. What is an ultra-wideband system? Short pulses transmitted across wide range of frequencies FCC regulations Spectrum greater than 25% of center frequency Frequency range from 3.1 – 10.6 GHz Source: University of Tokyo

4. Why Use Ultra-wideband? High data rates at short distances (more than 500 Mbps) Low power consumption Minimal interference with other devices

5. UWB Communication Scheme Pulse position modulation with time hopping A t 0 s 0 (t) t A 0 s 1 (t) t 0 A1A1 A2A2 A

6. UWB Communication Scheme transmitted signal channel impulse response AWGNreceived signal flexible multipath model

7. An Example, m=3 a ab ab 2 a,b – propagation constants ab 3 ab 4 ab 5 t A 0 h(t) * s 0 (t) t r(t) before added to n(t) aA abA ab 2 A ab 3 A ab 4 A ab 5 A 0 0 t s 1 (t) ab 2 A abA aA Received sample

8. Receiver Designs Examined Optimal Receiver Design Equal Combining Design Weighted Combining Design

9. Optimal Receiver Design Means of all samples known Values of channel propagation constants, a and b Lowest probability of bit error for given signal to noise ratio Problem: In reality, receiver does not know channel

10. Equal Combining Design Problem: Sample with small mean is weighted same as sample with large mean vs.

11. Equal Combining Design Performance As value of m increases, equal combining receiver performs poorly 3 dB 5 dB

12. Weighted Combining Design  Assign greater weights to samples with larger means  For example, if m=5 Z 0 and Z 5 are weighted by c 0 =1 Z 4 and Z 9 are weighted by c 4 vs. 0 < c < 1

13. Weighted Combining Design Performance At value of m=5, little improvement over equal combining But, as value of m increases, receiver performs better

14. How to improve design? Channel propagation constant b is not known Previously, set c=b because simulations showed low error rates By changing c over time, instead of having it fixed, better performance is possible

15. Observations and Conclusions As m increases, weighted receiver design has low bit error rates But there is room for improvement Would like to have low bit error rates for small value of m In better receiver, weighted coefficient c changes over time

16. Future Work Make c parameter adaptive to channel conditions Create more general channel models

17. Acknowledgements Dr. Baum Dr. Noneaker and Dr. Xu Clemson University NSF